Novel Breeding and Biotechnological Approaches to Mitigate the Effects of Heat Stress on Cotton

Abstract

High-temperature stress resulting from global warming is a major limiting factor for agriculture around the globe. Although cotton is a warmer-season crop, consistent high temperatures above optimal levels lead to various changes in morphological, physiological and biochemical characteristics of the plants that reduce the yield and quality of fibre. Breeding for thermotolerant cultivars is one of the best possible strategies to mitigate the adverse effect of heat stress. For this purpose, sufficient knowledge of plant response to heat stress, the mechanism of high-temperature tolerance and possible breeding strategies is imperative. All the stages of plant growth are affected by heat stress but the level of heat threshold varies at different stages. Heat stress may inhibit or reduce seed germination, causing poor seedlings and wilted roots at early stages, whereas at later stages it may adversely affect vegetative growth, reproductive growth, photosynthesis rate and cell membrane stability. Heat stress may also modulate the level of metabolites, hormones and reactive oxygen species (ROS). The expression of different heat shock proteins (HSP) varies with increase in temperature. In addition to HSPs, the cotton plant has various other mechanisms to cope with heat stress such as production of antioxidants for scavenging of ROS, maintenance of membrane stability, accumulation of compatible solutes and activation of various stress-responsive genes. A comprehensive understanding of traditional and advanced breeding and biotechnological approaches is required to improve heat tolerance in plants. There are many examples of plant improvement using traditional breeding approaches, but few achievements by utilizing biotechnological tools are reported, which is the result of very limited knowledge of molecular approaches and the genes related to heat tolerance. Conventional breeding approaches combined with biotechnological tools can provide opportunities to identify and incorporate genes related to stress tolerance for the development of new cultivars that can withstand high temperatures.